烯丙醇在Ti-MWW催化剂上的环氧化反应

以水热合成-酸处理法制得的T i-MWW分子筛为催化剂,研究了烯丙醇(AAL)和H2O2在水中的环氧化反应,考察了反应条件对AAL的转化率和环氧丙醇(GLY)选择性的影响。实验结果表明,AAL的浓度较低时有利于反应的进行,高浓度的H2O2则降低GLY的选择性,n(AAL)∶n(H2O2)=1时,GLY的选择性最高;当反应温度高于333K时,GLY的选择性随反应温度升高明显下降。当T i-MWW催化剂用量为50m g、AAL和H2O2的用量均为10mm ol、水量为20mL时,在333K下反应30m in,AAL的转化率达到96%,同时GLY的选择性可达98%以上。该反应的机理与TS-1催化剂催化烯烃环氧化反应类似,AAL和溶剂在活性位上存在竞争吸附。GLY的高选择性归因于T i-MWW催化剂中T i活性位与水、H2O2形成的五元环过渡态。

Epoxidation of Allyl Alcohol over Ti-MWW Molecular Sieve Catalyst

Ti-MWW molecular sieve catalyst were prepared by hydrothermal synthesis and acid treatment.Epoxidation of allyl alcohol(AAL)by H_2O_2 over Ti-MWW molecular sieve catalyst was studied using water as solvent.The lower concentration of allyl alcohol helped increase reaction rate and higher concentration of H_2O_2 decrease selectivity to glycidol.Under suitable conditions:reaction temperature 333K,reaction time 30min,Ti-MWW molecular sieve catalyst dosage 50mg,allyl alcohol 10mmol,H_2O_2 10mmol,and H_2O 20mL,conversion of allyl alcohol and selectivity to glycidol could reach 96% and 98%,respectively.Selectivity to glycidol was the highest when n(AAL) ∶n(H_2O_2)=1,but dropped quickly if reaction temperature increased above 333K.The reaction mechanism was similar to that of alkene epoxidation on TS-1 molecular sieve catalyst,which involved a transition state of a 5-membered ring formed through a solvent molecule or an allyl alcohol molecule on Ti active site.High selectivity to glycidol was attributed to high structural stability of Ti species and nature of the(5-membered) ring.